Wallboard or "drywall" panels are widely used in the building of relatively inexpensive and durable walls. The panels are normally manufactured in dimensions of 4'.times.8', 4'.times.9', 4'.times.10', 4'.times.12' and typically 3/8" or 1/2" in thickness, and are nailed or otherwise adhered to wooden or metal studs or concrete blocks which form a vertical support for the wall. Conventional drywall construction methods commonly involve applying a plurality of these wallboard panels to such a vertical support thus forming joints between the adjacent wallboard panels. While the wallboard panels themselves can be quickly nailed or otherwise fixed in place to form the wall, the joint between the individual panels normally must be concealed or "finished" before the wall can be painted or covered. "Finishing" refers to the task of providing a smooth, continuous finish to the joint area that is flush with the adjacent wallboard panels that need only be sanded lightly prior to painting or covering.
One commonly used form of wallboard panel is gypsum drywall that comprises a generally rectangular panel, the front surface of which has a substantially flat central or face surface and tapered marginal surfaces extending circumferentially about the edge of the panel. The tapered marginal surface typically starts at a distance of from about 21/2 to 3 inches from the panel edge and slopes downwardly to a maximum depth of from about 0.050 to about 0.070 inch. When the wallboard panels are erected in edgewise abutting relationship, the abutting edges of the adjacent panels collectively define a shallow V-shaped recessed area which extends along on both sides of the joint. This recessed area is commonly referred to as the "taper area".
A common method of finishing or concealing such joints comprises adhering over the joint a relatively narrow strip of paper, commonly referred to as "joint tape" by means of an aqueous gypsum cementitious adhesive, commonly referred to as "drywall mud". The width of the joint tape is typically slightly narrower than the dimension of the recessed area in the plane of the face surfaces of the wallboard panels. After the cementitious adhesive has been allowed to dry for about one day, another thin layer of the cementitious adhesive is applied over the taped joint, so that the intermediate product is a layer of cementitious adhesive being somewhat wider than the paper tape and tapered out to very thin edges. This second layer of adhesive is allowed to dry for about one day and then another thin layer of the cementitious adhesive, somewhat wider, is applied thereover. In this manner, a final substantially monolithic or flush wall surface appearance is provided and the complete surface may then be lightly sanded and subsequently covered with a decorative coating of paint or the like. This finishing operation is understandably quite time consuming and labor intensive. The particular joint finishing system used must have a smooth, substantially flat outer surface which is substantially level or coplanar with the face surfaces of the adjacent wallboard panels and somewhat wider than the taper area of the joint.
The joint tape provides reinforcing strength to the joint system and prevents cracking of the drywall mud adhesive applied over and along the joint. With this conventional technique for concealing or finishing drywall joints, there often develops a slight ridge or bead on the wall surface directly over the joint. This defect can mar the smooth appearance of the wall surface and costly repairs may be required to correct the condition.
As one can distill from the above discussion, this method of finishing joints requires a relatively long period of time due to the necessity of waiting about one day for each layer of adhesive to dry before the next layer can be applied. The drying times ensure that the job cannot be completed in less than 3-4 days. Sanding the dried mud plaster is both a tedious and unpleasant task and requires skill and patience as each of the three coats is usually required to dry at least 24 hours.
Oftentimes, as a worker is attempting to smooth and feather the mud compound on one panel surface near the joint line, an edge of his finishing tool inadvertently contacts the dry plaster compound previously applied and smoothed on the opposite panel surface, thereby leaving a blemish or mark in the plaster compound requiring the worker to go back and repair or "touch-up" that area, or causing small masses of the dry plaster compound to pull or break away from the dried plaster compound, such as in the form of chips or flakes, and mix with the wet plaster compound being applied to the opposite panel surface. The presence of the dry flakes in the wet plaster compound render providing a smooth finish thereto practically impossible. This can be a re-occurring nightmare for a worker as, while working on one panel surface, he must be sure not to contact the plaster compound applied to the opposing panel surface while still providing a continuous smooth surface between the taped area and the adjacent panel surface and along the junction line of the joint. This is a very labor-intensive process and persons skilled in the art readily appreciate the great amount skill required to achieve a smooth, continuous surface to the drywall compound applied to such joints.
Several prior attempts have been made to use various types of joint tape to cover the joint between adjacent wallboard panels. Examples of such attempts are U.S. Pat. Nos. 1,691,179; 1,936,317; 3,444,657; 3,576,091; 4,157,271; and 4,425,175.
U.S. Pat. No. 3,444,657 to Swanson describes a joint structure in which a molded plastic strip having a tapered cross-section fills the depressed tapered area along the joint. However, according to the system described in Swanson, the drywall panels must be of a special construction. The requirement for specially constructed wall panels limits the use of this type of strip to particular types of panels not generally available and, moreover, effectively precludes extensive commercial use of the system by individual construction companies and others.
U.S. Pat. No. 4,157,271 to Moore discloses a drywall joint filler including a flexible vinyl molded plastic strip with a central longitudinal spline intended to extend into the space between adjacent wallboard panels. The spline is equipped with spurs or whiskers to help secure the strip in place. The thickness of the strip decreases along its width to occupy the tapered depression area formed by the abutting wallboard panels. The strip is attached to the wallboard panels by double coated adhesive tape placed on opposite sides of the joint. In use, protective release paper is removed from the double-coated tape and the plastic strip is placed using the spline to locate the space between the wallboard panels and the strip is then pressed into place.
There remains a need, however, for an effective self-adhesive drywall finishing tape to maximize the economy and efficiency of wallboard finishing operations.